Electrically heated roll



Oct. 11, 1966 c. VAN TOORN 3,278,723

ELECTRICALLY HEATED ROLL Filed 001: 25, 1963 4 Sheets-Sheet l gamma 4%ATTORNEY.

Oct. 11, 1966 c. VAN TOORN 3,278,723

ELECTRICALLY HEATED ROLL Filed Oct. 25, 1963 4 Sheets-Sheet 2 INVENTOR.

CORNELIUS VAN TOORN BY @wmi ATTORNEY.

Oct. 11, 1966 c. VAN TOORN 3,278,723

I ELECTRICALLY HEATED ROLL Filed Oct. 25, 1963 4' Sheets-Sheet s j -#1 lE INVENTOR.

CORNELIUS VAN TOORN BY @a/wzf ATTORNEY.

Oct. 11, 1966 c. VAN TOORN 3,278,723

ELECTRICALLY HEATED ROLL Filed Oct. 25, 1963 4 Sheets-Sheet 4 I Q I 231s 2 5 2 354 .332

Q m. M. v s J Q A o n 5 1 V INVENTOR.

comvsuus VAN TOORN v 1 i 'QBY ATTORNEY.

United States Patent slgnor to B. F. Perkins & Son, Inc., Holyoke, Mass.Filed Oct. 25, 1963, Ser. No. 319,072 1 Claim. (Cl. 219-470) Thisinvention relates broadly to new and useful improvements in the heatingof rotatable rolls or cylinders or drums suitable for the drying and/orheat treating and/or ironing and/or polishing of continuous webs, bands,tapes, ribbons, filaments, yarns and other elongated articles, as in theproduction of paper, textiles or the like, and more particularly relatesto electrically-heated rolls wherewith operating efficiency and rapidand uniform heating and/or drying under conditions of accurate andconstant automatic temperature regulation are desiderata.

For various purposes, it is desirable to have a roll which may beuniformly and accurately heated throughout the entirety of itsperipheral surface or throughout a smaller portion thereof, and moreoverone in which the temperature may be selectively varied instantaneouslyand at will or otherwise positively controlled for employment inconnection with the drying of a web as it is being continuously advancedrelative thereto.

In the conditioning of certain materials with a heated roll,difliculties have consistently arisen in obtaining an even heating overthe entirety of the roll surface, especially in the case of a paper webwhere the paper functions as a heat conducting medium to draw thegenerated heat away from the roll.

In contrast with prior art systems teaching the heating of a solid or ahollow roll, by means of steam, oil, other medium in gas or liquid form,or electricity, where the heating elements are introduced centrally ofthe roll, this invention comprehends a heating system wherein thegenerated heat is conducted outwardly to the outer or finishingperipheral layer of the cylinder, so as to offer a resultant highefliciency contributed to in part by a new and novel system of rollconstruction and in part by a new and novel electrical/electroniccircuity to the end that the roll may be heated to and/or maintained ata desired temperature with greater speed and accuracy than has hithertobeen possible with rolls incorporating electric heating elements.

In broadest aspects, one primary object of the present invention is toprovide a roll having a hardened surface, and possessing structuralrigidity such as to withstand the enormous physical stresses to whichrolls of the comprehended types are normally subjected and to providemeans cooperant therewith for electrically heating the rollcharacterized by a provided reliable and eificient conductivity pathbetween the heat source and the roll surface whereby to maintain adesired temperature at the roll surface irrespective of whether or notthe roll is rotating and absent a large temperature differential betweenthe heat source and the roll surface and afiording uniform dryingthrough the entire length and/or width of the material in contacttherewith.

It is another object to provide means by which the roll temperatures maybe more dependably and uniformly regulated than has been heretoforepossible by virtue of the heating elements being strategicallypositioned closely adjacent the peripheral surface of the roll and beingrotatable therewith.

It is a further design hereof to provide a self-contained roll or drumor cylinder in the respect that it self-stores its heating elements ascontrasted with a roll or drum or cylinder heated by adventitious means.

It is a particularly salient object hereof to provide a roll which shallbe of uniform structure and density throughout its peripheral surface inorder to meet the exacting requirements dictated for such structures andto provide techniques of fabrication to insure that each roll shall bethe equal of each other roll thus to guarantee uniformity of work pieceswhen and as two or more of such rolls are unisonly employed.

Further describing the invention broadly, the electrical elements aredistributed over the roll periphery in manner to achieve a permanentmain heating system which supplies the entirety of the peripheralsurface of the heat roll with a given temperature under presetconditions, augmented :by a secondary or supplemental heat system whichis superimposed upon the permanent main heating system and isproportionally controlled to effect a supply of the superimposed balanceof heat to the surface.

In contradistinction to so-called rate control systems wherein, duringany change in the primary sensing circuity, the output is achieved by aninstantaneous overshooting action, herein is taught a proportionalcontrol system designed to effectuate at any given moment an output, themagnitude of which is at any moment proportional to its cause. Statedotherwise, by proportional control is envisioned that any change orvariation of magnitude in the sensing control circuity induces anamplification in the power system output which is distinctlyproportional to the change in the primary circuity. The feedback, as aninherent feature of this distinct proportional control, is strictlyphysical and is represented by a heat path between the outer layer ofthe heat roll and a thermistor, which is physically located in thisouter layer.

Among other advantages flowing from my invention may be mentioned thefact that the invention provides automatic compensation for heat demandwhich may vary in different applications according to the rate ofproduct travel, product size, moisture content, atmospheric conditionsor any practical combination of such factors or others not itemized, tothe end that by so providing means for controlling temperature and hencethe rate and degree of drying, the overall effect on the finishedproduct represents substantial improvements as compared with that ofsimilar products dried by any of the heretofore known prior-art dryingmethods.

My invention is particularly well adapted for embodiment in anelectrically-heated calender roll and a device of this character isshown in the drawings for purposes of illustration, although myinvention is by no means limited in this regard and may be applied tovarious other rotatable or otherwise movable :bodies.

In such instance of specific purpose, webs of paper are adapted to passover a series of rotating cylinders for the purpose of evaporatingmoisture from the web so that same leaves the last of the cylinders in adesired dried condition.

The distinguishing features of my invention, and the importantstructural elements characterizing the practical embodiments which areillustrated as examples, will be more particularly explained inconnection with the details of construction and operation which arefully brought out in the specific description following, when read inconjunction with the accompanying drawings, in which:

FIGS. 1 and 2 are side and front elevational views respectively ofcalender apparatus and showing a pair of cantilevered rotatable dryingrolls, embodying the novel features of the invention;

FIG. 3 is an axial cross-section of one form of roll for purposes ofillustrating one construction of heated roll of the invention;

FIG. 4 is a sectional view through the midsection of the roll shown inFIG. 3;

FIG. 5 is an axial cross-section of another form of roll construction;

in its respective mounting means.

'in turn, to elevate the respective mounting means.

FIG. 6 is a section-a1 view through the midsection of the roll shown in'FIG.

FIG. 7 is an axial cross-section of another form of roll construction;

FIG. 8 is a sectional view through the midsection of the roll shown inFIG. 7;

FIG. 9 is an axial cross-section of still another form of rollconstruction;

FIG. 10 is a sectional view through the midsection of the roll shown inFIG. 9;

FIGS. 11- 13 are schematic views of rolls illustrating variouscombinations of an arrangement of main or buildup circuit and modulatedcircuit superimposed thereover adjacent the respective outer peripheriesthereof; and

FIG. 14 is a wiring diagram of a complete circuit of the proportionallyelectronically controlled loa-d adaptable for employment with any of thevarious roll constructions of the invention.

Referring now to the drawings more in detail, the novel features of theinvention will be described.

In FIGS. 1 and 2, a calender is shown incorporating side frames 2 of apair which may take various forms and, in the usual situation, aresecured on foundations and held in transversely spaced relation as toeach other by transverse members (not shown) secured thereto.

An upper drive roll represented by 4, has opposite end journal portions6, each rotatable in a bearing housing 8 of the respective side frame,in known manner.

A drive motor having a drive sprocket and associated drive chain, noneof which are shown, is connected to a sprocket 10 of one of the endjournal portions 6 of drive 'roll 4. Any equivalent drive means whichwill continuvertically-sliding engagement and is held stationarilyrelative to its respective column as a gib 16 secured thereto andengageable with a rear side of the respective column.

A driven roll 18 may have opposite end portions, called hollow shifts20, each rotatable in suitable bearing means Alternatively, a unitaryhollow shaft may be provided which will extend longitudinally of andoutboard of the opposite roll extremities.

The mounting means 14 may be unisonly elevated by any appropriate meansto engage the. supported driven roll 18 with drive roll 4. Forillustrative purposes, a cylinder 22 in which a plunger 24 isreciprocable may be provided for each mounting means. Pressureintroduced via a cylinder inlet 26 to motivate the plunger will serve,Each cylinder 22 may be supported by an outwardly-extending portion 28of the respective side frame.

A housing 30 is fixedly secured to one of the mountings 14 as by bolts32 or the like, and an electric motor '34 may be associated with thehousing 30 and suitably secured thereto.

A calender, thus described, being more or less conventional, furtherexemplificatio-n is not considered to be essential.

Conventionally, slip rings are employed to provide the electricalconnections between a stationary member, such as a housing 30, and arotative member, such as a driven [roll 18.

' fabrication of a calender roll which can be electrically heated withthe successful effort being made to provide a concentration of the rollmass in or as near as possible to the heated surface.

In each of FIGS. 3, 5, 7 and 9 the basic construction will be observedto comprise an axially-bored cylinder,

cooled by the center cooled shaft.

generally indicate-d by 200, comprising the roll proper, and includingin each case a core section 202, usually formed of steel and havingwalls which thicken linearly from each roll end toward an intermediateor central bore section, as shown, with a support shaft 204 beingpress-fitted into the bore and keyed to the core section in conventionalmanner to preclude separate rotation of shaft and roll.

The connection between core section and shaft constitutes the mechanicalconnection of the roll to the shaft, which connection acts as the onlyheat path between the roll structure per se and its cooperant shaft andalso allows a cantilever effect.

Bearings 208, 210, preferentially of spherical roller self-aligning typeare provided on the shaft at opposite sides of the roll.

The shaft is bored as at 206 to allow for shaft cooling as well as thecooling of bearings 208, 210.

An air cooling system (not shown) may be incorporated therewith andenvisions a forcement of a supply of a gaseous fluid, such as compressedair from an outside source through the center bore from the left handend, as viewed in FIGS. 3, 5, 7 and 9 wherefore bearing 208 is Bearing210 is not directly air cooled as the coolant flows radially from theshaft bore to the outer surface thereof through a plurality of radiallyextending coolant apertures 212 disposed in a transaxial plane in frontof bearing 210 wherewith heat conduction along the shaft toward thisbearing is opposed by means of a roll retaining sleeve 214 concentricwith and spaced from the shaft and enclosing same in manner so as toforce the coolant to flow in a counter direction through a plurality ofcircularly-arranged longitudinally- 'sidual heat would travel from theroll to the shaft and bearings and housing with a concomitant increasein the radiation area and a consequent disturbance of the equilibriumzone.

At the opposite end of the shaft, an air sealing plug 218 is disposed.

With more specific reference to FIGS. 3 and 4, roll 200 therein will beobserved to be constituted in main by the previously described coresection 202.

In fabrication, the outer peripheral surface is first rough machined toa predetermined diameter and is then again so machined as to provide aplurality of semi-round or parti circular recesses or grooves in spacedparallel relationship as to each other around the roll periphery andcoaxial of the roll axis.

Each such recess is coated with a layer of an inorganic material such asaluminum silicate or equivalent cementious material preliminary to theseating therewithin of a section of a sinuously extending heatingelement or electrical conductor generally indicated by 220. Saidconductor is sinuously wound back and forth in each of the recessesaround the roll periphery.

The conductor comprises a central conductor or resistance heat wire 222,preferably of copper, embedded in an insulatingmedium 224, preferablyconsisting of a mass of a refractive oxide, for example magnesium, whichis extruded or otherwise formed over the central conductor 'to form acovering thereover, the whole being surrounded by a metallic retainingsheathing or covering 226 of a ductile metal such as copper tightlyencasing the coated tioned, may be operatively secured relative to theroll as by a brazing to be held Within the respective recesses againstaccidental derangement during the subsequent spraying operation.

A thin uniform layer of copper 230 is then sprayed, electroplated orotherwise applied, over the roll periphery and the upper exposedportions of the sections of the heating element supported thereby.

If spraying is the employed system, same may be by means of an atomizinggun with the metal being melted and the molten metal being atomized bymeans of an air blast and directed to the surface to be coated.

Where the metal to be deposited is in a powder form, a finely dividedmetallic powder may be heated to its melting point by blowing it throughthe flame of a blow pipe with the resulting spray being projected by anair blast toward and onto the roll.

The minute semi-molten particles constituting the spray acquire asuperficial oxide coating which become incorporated into the coatingbeing laid down, the impinging particles of metal being flattened intorelatively thin half .molten scales by virtue of the rapid deposition.As the coating is built up, these scales become interlocked with otherspreceding and succeeding same so as to allow a structure of highintrinsic tenacity, which covers the interfaces and the exposed portionsof the core section between the sections of the heating elementwherefore the metal in effect brazes itself to the base metal of thecore section and the sheathing of the heating elements so as to allow astrong mechanical bond in the form of a high heat conductive layer inwhich the sections of the electrical element are encapsulated, theybeing fused solidly therein the said layer, thereby is constituted asuperior conductive medium permitting a uniform and controllabledistribution of heat throughout the entirety of the roll peripherycapable of withstanding conditions of excessive heating followed bydrastic cooling as may be normally expected to be encountered.

There following, a layer 240 constituted by fused colmonoy is spraywelded to the outermost surface of layer 230 to provide a hard outermostworking surface, the hardness thereof being according to anticipatedrequirements.

With more specific reference to FIGS. 5 and 6 roll, 200 constituted bythe previously described core section 202, is first rough machined to apredetermined diameter and is then further machined to provide acircumferentiallylocated helically-arranged semi-roundcontinuous-fromend-to-end recess or groove around the roll periphery, inwhich recess is spirally wound a length of a heating element comprisinga length of metallic tubing 250 such as of copper or stainless steelencapsulating a length of a conductor or resistance heat wire 252.

Thereafter, the heating element, so spirally positioned, may be securedrelative to the roll as by a brazing to prevent same from movementduring the subsequent spraying operation.

A thin uniform layer 256 of copper is then sprayed, electroplated orotherwise applied over the roll periphery and the upper exposed portionsof the heating element supported thereby.

There with is formed a high heat conductive layer in which theelectrical element is encapsulated by being fused solidly therein, theformed layer constituting a superior conductive medium allowing auniform and controllable distribution of heat throughout the entire rollperiphery.

There following, a layer 258 constituted by fused colmony is spraywelded as an outermost finished layer of a hardness desired.

Said layer 258 preferentially will have been first partly fused by anatomizing means followed by a fusion via means of a high frequencycurrent.

With more specific reference to FIGS. 7 and 8, roll 200 comprising thecore section 202 is first rough machined to a predetermined diameter andis then machined to provide a circumferentially-locatedhelically-arranged continuous-from-end-to-end semi-round recess. Therecess may be preliminarily conditioned by the coating with a layer ofthe above described inorganic cementious material such as aluminumsilicate.

In said recess, a length of a heating element comprising a length ofmetallic tubing 260 such as of copper and incorporating a length of aresistance wire 262 is spirally wound.

A plurality of uniform layers 266 of chrome are then bombarded, eachlayer being bombarded from a different angle during an electroplatingprocedure designed to allow a finished surface of a desired hardness andadequately covering the roll periphery and the upper exposed portions ofthe heating element supported thereby.

With more specific reference to FIGS. 9 and 10 roll 200 constituted bycore section 202, is shown in its upper half portion, as illustrated, asbeing provided with a deep seated spirally-arranged groovecircumferentially of the roll in which a continuous length of a heatingelement called a main source and comprising a copper tubing 270 sheathedaround a resistance wire 272 is seated. Superimposed over the mainsource heating element in a portion only of the groove is a continuouslength of a heating element comprising a copper tubing 274 sheathedaround a resistance wire 276, which heating element will serve as theheating element of one of the proportionately controlled zonesidentified as A, with another similar heating element superimposed overthe main source heating element in a different portion of the grooverepresentative of the proportionately controlled zone B.

With the heating elements in situ in superimposed arrangement, thegroove may be swaged as by a forcing tool P so as to cause the walls ofthe groove to be pressed inwardly in an encapsulating manner on theheating elements.

A thin uniform partly fused layer 280 of colmonoy is then spray weldedover the roll periphery and any exposed portions of the heating elementssupported thereby.

Therewith is formed a high heat conductive layer in which the electricalelements are encapsulated, they being fused solidly therein the layerconstitutes a superior conductive medium allowing a uniform andcontrollable distribution of heat throughout the entire roll peripheryand allowing excessive heating followed by drastic cooling, workingconditions normally expected to be encountered.

There following, a layer 282 constituted by fused colmonoy is spraywelded over the layer 280 and is given a outermost finish by a highfrequency means to offer a desired hardness according to anticipatedrequirements.

In the lower half portion of core section, identified as 202, as shownin FIGS. 9 and 10, said core section is envisioned as comprising amehonite casting having a smooth mirrored outer peripheral surface andprovided with a plurality of longitudinally-extending openings therethrough in spaced parallel relationship to each other adjacent to theroll periphery, in each of which openings a heating element 290 isseated, same comprising a boron bar capable of forming its own skin uponsintering so as to provide its own integral electrical insulating layer,and being coupled as by a coupling 292 to an electrical conductor 294,only one of which, at one end of the bar, is shown.

This invention envisions that a permanent or main circuity including itsroll heating elements may be employed above, so as to supply a giventemperature to the outer roll surface, as comprehended in theexemplifications in FIGS. 3 and 4, 5 and 6 and 7 and 8, and furtherenvisions that in other applications, such as illustrated in theexemplification in the upper half section of FIGS. 9 and 10, incombination with said permanent or main circuity, a proportional heatmodulated controlled circuity including its roll heating elements may beemployed by superimposition thereover.

Such proportional heat modulated control circuit may be superimposedover the entirety of the roll surface or a plurality of such circuitsmay be each superimposed over a portion or zone of the roll surface, aswill be hereinafiter discussed in detail.

Such proportional heat modulated zone control system is achieved by thedesired number of electric-electronic control cireuities.

The roll or each Zone thereof will incorporate its owntemperature-sensing device designed to trigger an oscillating circuityforming an integral part of the entire electrical-electronic control andpower circuity, now to be described in connection with FIG. 14 whereinis defined a direct current circuity, although it will be understoodthat the principles may be employed in connection with an alternatingcurrent circuity.

A voltage, 60 cycle alternating current, emanating from a current supplysource (not shown) leads via leads 300, 302 to a full wave bridgerectifier, generally indicated by 304, and constituted by four matchedrectifier cells 306, with leads 308, 310 leading from the rectifier tothe other instrumentalities of the electric-electronic circuit.

A resistor 312 is provided along lead 308 and a Zener voltage regulatingdiode 314 is connected across leads 308, 310. A unijunction transistor,generally indicated by 316 is connected across leads 308, 310 throughresistors 318 and 320 and constitutes a three-terminal semiconductordevice including the usual base-one and base two ohmic contact andsemi-conductive bar to which is made a single rectifying contact by anemitter 322. Transistor 316 is a unilaterally conducting device, onebase or terminal of which is negative with respect to the other forallowing current flow from one base to the other.

A PNP transistor, generally indicated by 324, is connected across leads308, 310 through resistors 326 and 328 and is arranged in commoncollector configuration with an emitter base 330, a collector base 332,and a base 334.

A power capacitor 336 is disposed in series with resistors 326 and 328and transistor 324, with the transistor serving as a variable resistorupon changes in the base voltage.

A thermistor, generally indicated by 338, is connected across lead 308and the common terminal 340 of the said thermistor, base 334 oftransistor 324, and a cadmium sulphide cell 342.

The opposite side of cell 342 is connected to lead 310 along which anadjustable variable resistor or rheostat 344 is provided.

A lead 346 connects between the common connection of capacitor 336 andresistor 328 and emitter 322 of unijunction transistor 316, and a lead348.

A lead 390 connects between the common connection of unijunctiontransistor 316 and resistor 320 and the gate 350 of a current triggeredsilicone controlled rectifier, generally indicated by 352, which isconnected across leads 308, 310 in series with a load L, such as a roll.

Rectifier 352 has three terminals, an anode 354, a cathode 356, and saidgate 350.

Leads 360, 362 lead from an alternating current source to a light sourcecircuit supply transformer, generally indicated by 364, the oppositeside of which transformer is connected by leads 366, 368 to a lightsource 370 with a light intensity (temperature control) variableresistor or rheostat 372 disposed in lead 368 for controlling thevoltage of the filament in the light source and thereby the intensitythereof.

A pyrometer 374 is provided along lead 308.

The operation of the circuits in the exemplification may be defined asfollows.

Rectifier 304 converts the 60 cycle AC. voltage, impressed via leads300, 302, to pulsating DC. voltage, ultimately applied to load L (theheating element in the 'roll or a zone thereof).

The pulsating DC voltage is applied along lead line ambienttemperatures,

308 through resistor 312 and Zener voltage regulating diode 314 inseries therewith and serving to hold the voltage relatively constantly,despite any sustained D.C. voltage variations, and serving also as thesupply voltage for unijunction transistor 316 and PNP transistor 324.

Unijunction transistor 316, suited for use in the go-nogo type ofvoltage sensing here contemplated, functions to fire rectifier 352. Whenits emitter voltage is less than a predetermined limit, the emitter isreverse-biased wherefore only a small emitter leakage current flows, butwhen it is greater than said limit, the emitter is forward-biasedWherefore the emitter current flows. As the emitter current increases,the emitter voltage decreases wherefore a negative resistancecharacteristic is attained.

If the input sign-a1 is negative, the unijunction transistor will fireso as to trigger the pulse sensitive rectifier 352, said rectifierallowing current to pass therethrough according to the supplied triggervoltage on its gate. Pulses will occur at the output of the unijunctiontransistor so long as the input signal remains positive, the outputpulses being suflicient to trigger the pulse sensitive rectifier.

Thermistor 338 is a temperature-dependent resistor with a high negativetemperature coeflicient of resistance designed for exposure to thermalheat, as contrasted with normal resistors not so exposed to temperature,save for and responds to temperature changes sensed at the outer rollsurface by effecting changes in the current flow.

In operative use, as heat is applied to the work load so as to increasethe temperature thereof, the resistance is lowered. Stated otherwise, asthe work load becomes more heated, the easier it conducts. Conversely,as the temperature of the work load decreases, the resistance is raised,in direct opposition to the effect of temperature changes on metals.

The collector current of the PNP transistor is controlled by the currentin the base circuit which is in turn determined by the resistance of thethermistor, variable with the temperature, as aforesaid. Accordingly,the collector current likewise varies with the load temperaturewherefore the PNP transistor serves as a variable resistance with valuesproportional to the load temperature (the temperature of the roll).

The capacitor functions as a timing capacitor for the unijunctiontransistor and is charged by the PNP transistor.

As the thermistor varies with the load temperature, the capacitorcharges faster or slower as the resistance of the thermistor decreasesor increases respectively.

With a direct current voltage impressed across leads 308, 310, thecharge on the capacitor builds up to the peak point of the emittervoltage of the unijunction transistor and the PNP transistor assumes anegative resistance characteristic.

When the voltage on the capacitor just exceeds the peak point of theemitter voltage of the unijunction transistor, the emitter becomesforward-biased so as to cause the capacitor to discharge producing apositive pulse at the gate of the rectifier so as to trigger same by wayof releasing from its blocking state so that current will flowtherethrough.

After such discharge by the capacitor, the emitter of the unijunctiontransistor reverts back to its reversebiased state, and the cycle isthen repeated.

The rectifier functions as a conventional rectifier modified to theextent that it blocks in a forward direction until a small signal isapplied to its gate. Until a pulse from the capacitor arrives at itsgate, the rectifier remains in the blocking state. After the gate signalis applied, the rectifier conducts in the forward direction andcontinues conduction, even after the gate signal is removed.

If the instantaneous voltage is high enough to make the load currentequal to or greater than the sustaining current, the rectifier willremain in the conducting state for the rest of the cycle. If it is nothigh enough, the

current may decrease until the next pulse arrives, when theinstantaneous voltage may be high enough to sustain the current.

The rectifier may thus be observed to be turned on and oil 120 times persecond according to the pulsating voltage applied thereto which reacheszero 120 times per second, and each time the voltage s-o reaches zero,the rectifier assumes its blocking state and can only be turned on whenanother appropriate pulse arrives at its gate.

Therefor, the later in the cycle that the pulse arrives, the later therectifier will be turned on, and accordingly the rectifier can be madeto conduct for only a small part of a cycle or for a large part thereof.

The rectifier will stop conducting, if the current passing therethroughfalls below its sustaining value; that is if the voltage across it fallsbelow a predetermined critical value.

As a matter of actual practice, the conduction of the rectifier can becontrolled by varying the thermistor within a range from between acompletely-turned-oif position to a substantially full time conduction(180 degree angle of conduction).

If the roll or load is operating at a fixed temperature and thetemperature rises, the resistance of the thermistor decreases and thetransistor base bias current falls, so that in turn the collectorcurrent decreases and the resistance increases. The average power in theload (the heaters) then drops and the temperature falls back toward itsoriginal value.

The opposite effect ensues if the operating temperature at the rolldrops below the preset level.

If the temperature at the thermistor drops below the preset value, theresistance of the thermistor increases and the voltage flow at the baseof PNP transistor decreases to cause more base and collector current toflow so as to charge the capacitor more quickly wherefor the unijunctiontransistor is caused to fire the silicon controlled rectifier so that inturn more power is thus applied to the heater to enable the temperatureto return to the preset value. The reverse action takes place when andas the temperature attempts to rise above the preset value.

The cadmium sulphide cell acting as a light controlled rheostat isphysically located within a suitable protective tubing (not shown) onthe roll shaft, and the light source is located on a mounting (notshown) carried by the housing. The components are movable with respectto each other though they are not in physical contact with each other,their only interconnection being via the light beam directed by thelight source toward the cell.

The fixed operating temperature is controlled by the cell, suchoperating temperature being maintained relatively constant by the actionof the thermistor.

The light source provides a means for over-riding the manual temperaturecontrol device in the following manner. The resistance of the cellvaries according to the intensity of the light directed thereonto so asto provide a control resistance on the roll proportional to the lightsource intensity.

Like the thermistor, the cell forms a voltage divider which provides abias for the base of the PNP transistor, but unlike the thermistor, itsresistance is varied by varying the intensity of light shining thereon.

Interconnected within the thermistor circuit is a temperature readingdevice or pyrometer, mounted on the housing, to provide intelligence asto the fixed temperature of the roll surface or of any of its zones.

With the exception of the thermistor, located beneath the outerperipheral surface of the roll, and the cell, located on the roll shaft,the balance of the electronic components are engaged with the shaft inmanner wherefor the flow of coolant through the shaft is utilized forcooling the transistors, diodes, silicone controlled rectifiers andassociated components.

In the three illustrative examples of windings of a permanent or maincircuity and a superimposed secondary proportionally controlled circuityshown in FIGS. 11-13, the principles of supplying the entirety of theroll surface with a given temperature under pre-set conditions,augmented by a secondary system proportionally controlled to effect asupply of the superimposed balance of heat to the surface areexemplified by a variety of arrangements.

With the main circuity being incapable of holding a constant temperaturedue to the dissipating action of the paper or other web being passedthereover, the superimposed modulated control means allows a completelyautomatically controlled means so as to provide a constant temperatureof determined value regardless of the conditions encountered by the maincircuity.

In essence, the additional or secondary circuit is only necessary asmore heat may be called for at the roll surface, and advantageously whenand as the added power is required to provide the additional heat. Thecircuit etfectuates at any given moment an output, the magnitude ofwhich is proportional to its cause. Any change in mag nitude, sensed bythe sensing mechanism in the secondary circuit, induces an amplificationin the power system output which is distinctly proportional to thechange in the primary circuity.

In FIG. 11, a main circuity represented by dotted lines is shown asbeing spirally wound circumferentially of a roll and a secondaryproportionally controlled modulated circuity represented by a solid lineis shown as being sinuously wound axially of the roll and around theentirety of its periphery in a back and forth manner.

In FIG. 12, a main circuity represented by a solid line is shown asbeing spirally wound circumferentially of the roll and a series ofsecondary modulated circuities represented by dotted lines are shown asbeing each spirally wound circumferentially of the roll and in a side byside manner as to each other so as to cover different zones of the roll,it being understood of course that these zones can be of varying sizesas to each other.

That is, a zone, as the term is here employed, may comprise the entireroll periphery or a predetermined portion thereof, the heat controlbeing accomplished by means of a plurality of circuities, one of themain heating system and one or more electric-electronic controlcircuities, there being one for each such zones inclusive of its owntemperature-sensing-and-triggering mechanism and its owntemperature-controlled electronic power source, by all of which means, ahighly effective distribution of heat upon the roll surface isachievable. More particularly, the system can be so adjusted that atdifferent zones of the roll, different heat conditions may be maintainedaccording to the dictates found to be the optimum for that particularzone of the roll when drying any particular type of work.

In FIG. 13, a main circuity represented by a solid line is shown asbeing spirally wound circumferentially of the roll and a series ofsecondary modulated circuities represented by dotted lines are shownbeing each sinuouslv wound circumferentially of the roll and over aportion or zone of the periphery thereof.

I claim:

An electrically-heated roll comprising a rotatively mounted cylinder,means for turning said cylinder, a main helically wound resistance wireextending lengthwise of and within the out-er wall of said cylinder, aseries of zigzag secondary resistance wires extending lengthwise of saidcylinder and arranged in spaced relation as to each other around saidcylinder and in superimposed relation upon said main resistance wire, aplurality of collector rings disposed adjacent said cylinder, said mainand secondary resistance wires being electrically connected to saidcollector rings, a source of electric energy, and connections betweensaid collector rings and source of electrical energy.

(References on following page) 11 12 References Cited by the Examiner3,020,383 2/ 1962 Tsuneo Onishi et a1. 219470 3,037,106 5/1962 Seney210-471 UNITED STATES PATENTS Allen 3 :33; ANTHONY BARTIS, ActingPrimary Examiner. Carl 9 Malewski 1 219 470 5 RICHARD M. WOOD, Examzner.

L. H. BENDER, Assistant Examiner.

Keen et a1 219-21 0

